Non-directional oriented silicon-iron



Oct. 30, 1962 .1. M. JACKSON 3,061,486

NON-DIRECTIONAL ORIENTED SILICON-IRON Filed Dec. 30. 1957 3 IN V EN TOR.

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United States Patent 3 061 486 NON-DIRECTIONAL ORIENTED SILICON-IRON John M. Jackson, Middletown, Ohio, assignor to Armco Steel Corporation, Middletown, Ohio, a corporation of Ohio Filed Dec. 30, 1957, Ser. No. 706,091 7 Claims. (Cl. 148-111) Silicon-iron sheet stocks having a high degree of preferred orientation have come into wide spread commercial use. For the most part, such silicon-iron sheet stocks have had a crystal orientation which may be designated as (110) [001] in the standard notation of Millers indices; and the products have exhibited a high permeability in the rolling or straight-grain direction, but a poor permeability in all other directions.

There are numerous uses for silicon-iron sheet stocks in which a highly directional permeability is not desired. For example, in rotating electrical machinery Where the laminations are punched as one piece, it would be of great advantage if the permeability could be made both high and substantially equal in all directions in the plane of the sheet stocks. So far as is known, this has never hitherto been accomplished in practice. Where a substantially equal permeability has been desired in all directions within the plane of the sheet stock, the practical art has endeavored to meet the need by producing stock characterized by random crystal orientation. The permeabilities in the various directions may be substantially equal in a randomly oriented material; but the permeabilities will be relatively low in all directions because of the random orientation. It is a primary object of this invention to provide a silicon-iron sheet stock having a nondirectional permeability which is at the same time a higher permeability than has hitherto been obtainable in such material.

So far as is known, the art has not hitherto been able to utilize any aspect of crystal orientation in the manufacture of truly non-directional silicon-iron sheet stock. It is also a fundamental object of this invention to provide a non-directional product, and a process of making it, wherein crystal orientation is employed to increase the permeability in all directions in the plane of the sheet stock.

These and other objects of the invention which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, are accomplished in that product and method of making it of which an exemplary embodiment will hereinafter be described. Reference is made to the accompanying drawings wherein:

FIGURE 1 is an X-ray pole density stereogram of (100) planes showing the orientation of the starting material employed in this invention.

FIGURE 2 is an optical stereographic projection of the (100) planes in the product of this invention, which in manufacture has been cold reduced 70% and annealed at a high temperature in hydrogen.

The invention is based on the concept that if in a silicon-iron sheet stock the cubic crystals are so oriented that certain faces of the crystals lie parallel to the surfaces of the sheet stock while the cube edges which bound the said faces have a random orientation, the permeability will not only be substantially the same in all directions within the plane of the sheet but will also be substantially higher in all of these directions than that which can be obtained with a wholly random crystal orientation. The translation of this concept into actual practice, involves two problems: first the provision of a starting material characterized by the crystal orientation just described, and second the successful reduction of the starting material to final thickness by rolling, followed by annealing, with the preservation of the said orientation, i.e. with the avoidance of the production of some other orientation which would impart substantial directional properties to the product.

When molten silicon-iron is solidified against a planar cooling surface, crystals will form and grow against that surface having a cube face parallel thereto, but having no preferred orientation in any other direction. In other words, when silicon-iron alloy solidifies against a plane surface, a fiber texture is produced having the fiber axis in the same direction as the heat flow, and the (100) plane normal to the fiber axis.

If the silicon-iron is cast, say, into an ingot mold having substantially equal transverse dimensions, it will be evident that portions of the ingot will have the stated crystal orientation related to each of the four lateral walls of the mold. The result of hot rolling such an ingot will therefore be to produce a hot rolled material substantially characterized by a random crystal orientation. However, if the silicon-iron alloy is cast in a mold in which the length and breadth are both many times the thickness, the resultant casting will be characterized by the desired orientation excepting at the edges. It is possible to minimize the edge effect by insulation at the edges of the mold; but in any event the edge portions of the casting may be trimmed oif before the material is rolled. Thus it becomes possible to make relatively thin, slab-like material for hot rolling which is characterized by the desired orient'ation.

The desired orientation can be produced even more cheaply and conveniently by utilizing a continuous casting apparatus and method which result in the production of endless lengths of relatively thin materials (say half an inch or less in thickness), having a width many times greater (say at least twenty times) than their thickness. While there are many types of direct casting equipment which may be employed, reference is made for an exemplary showing to United States Patent No. 2,640,235 issued June 2, 1953, in the name of C. W. Hazelett. Such a machine is capable of producing castings of sheet width in thicknesses ranging generally from 0.1 to 0.5 inch in thickness, and in indefinite lengths which are advantageous for the purposes of this invention, although these dimensions are not limiting.

Cast material having the described orientation is capable of being hot rolled without losing that orientation. If, however, the material is formed by direct casting as a thin enough product it becomes possible to carry on the remainder of the reduction by cold rolling. The cast material may be subjected to a conventional anneal before cold rolling.

The result of cold rolling a silicon-iron alloy sheet stock is normally to elongate and partially fragmentize the grains, tilting them also in the direction of rolling. The highly oriented, highly directional silicon-iron products of the prior art have been made by subjecting the silicon-iron to one or more stages of cold rolling with intermediate and final anneals. The amount of the cold rolling is important. It is believed that the cold rolling tilts the grains or crystals into high energy positions, the subsequent heat treatments causing the crystals to assume some related low energy position, whereby a high degree of preferred orientation is produced.

In the practice of the present invention, where the starting material is either a hot rolled or a cast material in which the planes of the crystals are parallel with the sheet surface, it has been found possible to subject the material to a substantial cold rolling treatment followed by an anneal without essentially altering the crystal orientation. While not wishing to be bound by theory, it is believed that any high energy position to which the crystals are tilted still has the original orientation as its related low energy position. But the amount of cold work which may be done is critical. It has been found that 70% reduction is optimum for about 3% silicon content. If the reduction is diminished to 60% or increased to 80%, departures from the desired orientation begin to become apparent upon X-ray analysis. Consequently the range for the cold reduction is given herein as from substantially 60% to substantially 80%, for silicon-iron containing about 2.90 to 330% silicon.

By way of example of a specific material to which the invention has been applied, the following is given:

C .024 Mn .082

S .018 Si 2.90

Balance being substantially all iron.

It should be understood, however, that this analysis is exemplary merely and not limiting. The invention may be applied to silicon-iron alloys containing from about 2. to 3.5% silicon. As the amount of silicon decreases, the amount of cold work which may be done increases. Thus, as an over-all range of cold reduction commensurate with the last mentioned range of silicon content, from about 55 to 85% is given.

The other ingredients may vary substantially, particularly in view of the use to which the product may be put. Where a low carbon content is desired, say .007% or less, decarburization may be practiced in conjunction with any annealing treatment to which the material is subjected in accordance with known practices. The manganese content will usually lie between 0.004% and 0.40%.

After the cold rolling, the material is annealed, preferably in hydrogen, at temperatures between substantially 1400 F. and 2200 F.

Materials having the formula shown herein and treated as above described have exhibited straight-grain permeabilities at H =l0 oersteds of 1550, cross-grain permeabilities of 1520, and only slightly lower permeabilities in directions lying between the straight-grain and crossgrain. FIGURE 2 of the drawing is illustrative of the crystal orientation of these materials as determined by the optical goniometer. FIGURE 1 is an X-ray pole figure of the cast material, indicating that the orientation is substantially identical.

It is characteristic of the cold rolling and annealing treatments hereinabove described, when applied to material having the described initial orientation, that they may be repeated on the product without changing its essential orientation. In other words, if the hot rolled or cast gauge is such that more than one cold rolling treatment is desired to carry it to final gauge, a plurality of such treatments may be performed providing each such treatment embodies a cold rolling with a reduction as hereinabove set forth, and providing each such treatment is followed by the described anneal. The annealing treatments herein described may be box anneals or open anneals as desired. By an open anneal is meant a heat treatment in which the material in single strand or sheet form is sent through an elongated furnace in which both sides of the material are open to the atmosphere of the furnace, which atmosphere, however, is preferably a non-carburiz ing reducing atmosphere.

Modifications may be made in the invention without departing from the spirit of it. The invention having been described in certain exemplary embodiments what is claimed as new and desired to be secured by Letters Patent is:

1. A process of producing cold rolled silicon-iron alloy sheet stock containing 2% to 3.5% silicon, characterized by a grain orientation in which the (100) planes of the crystals are substantially parallel to the sheet surface and the edges of the crystals are randomly oriented in the plane of the stock, which comprises essentially the steps of forming a casting the width of which is at least about 20 times the thickness thereof, rolling the entire casting to sheet gauges in the direction of its greatest dimension, said rolling comprising at least one cold reduction, each cold reduction serving to reduce the thickness of said material from 55% to 85%, and annealing said sheet material at the final gauge at a temperature between l400 and 2200 F. in a non-carburizing reducing atmosphere.

2. The process claimed in claim 1 wherein the siliconiron contains about 2.90 to about 3.30% silicon, and in which the cold reduction is substantially to 3. The process claimed in claim 1 in which the initial stock is formed by casting the silicon-iron between substantially parallel cooling surfaces, and the cast alloy is hot rolled to an intermediate gauge prior to cold rolling.

4. The process claimed in claim 1 in which the initial stock is formed by continuously casting said stock into strip having a thickness of substantially 0.5 to 0.1 inch.

5. The process claimed in claim 3 in which the hot rolled alloy is subjected to an annealing treatment prior to cold rolling.

6. The process claimed in claim 4 in which the continuously cast material is hot rolled to an intermediate gauge prior to cold rolling.

7. The process claimed in claim 6 in which the hot rolled alloy is subjected to an annealing treatment prior to cold rolling.

References Cited in the file of this patent UNITED STATES PATENTS 2,053,162 Pfalzgratf Sept. 1, 1936 2,158,065 Cole et al May 16, 1939 2,327,256 Fowle et al Aug. 17, 1943 2,512,358 McGeary June 20, 1950 2,578,407 Ebeling Dec. 11, 1951 2,640,235 Hazelett June 2, 1953 2,826,520 Rickett Mar. 11, 1958 2,867,557 Crede Jan. 6, 1959 2,891,883 Howe June 23, 1959 2,943,007 Walter et al June 28, 1960 FOREIGN PATENTS 1,009,214 Germany May 29, 1957 

1. A PROCESS OF PRODUCING COLD ROLLED SILICON-IRON ALLOY SHEET STOCK CONTAINING 2% TO 3.5% SILICON, CHARACTERIZED BY A GRAIN ORIENTATION IN WHICH THE (100) PLANES OF THE CRYSTALS ARE SUBSTANTIALLY PARALLEL TO THE SHEET SURFACE AND THE EDGES OF THE CYSTALS ATR RANDOMLY ORIENTED IN THE PLANE OF THE STOCK, WHICH COMPRISES ESSENTIALLY THE STEPS OF FORMIMG A CASTING THE WIDTH OF WHICH IS AT LEAST ABOUT 20 TIMES THE THICKNESS THEREOF, ROLLING THE ENTIRE CASTING TO SHEET GAUGES IN THE DIRECTION OF ITS GREATEST DIMENSION, SAID ROLLING COMPRISING AT LEAST ONE COLD REDUCTION, EACH COLD REDUCTION SERVING TO REDUCE THE THICKNESS OF SAID MATERIAL FROM 55% TO 85%, AND ANNEALING SAID SHEET MATERIAL AT THE FINAL GAUGE AT A TEMPERATURE BETWEEN 1400* AND 2200* F. IN A NON-CARBURIZING REDUCING AT MOSPHERE. 